To obtain wear resistant steel, it is a common practice, for imparting higher wear resistance by providing a martensite single phase microstructure, to increase the amount of solute C so as to increase the hardness of the martensite microstructure itself. In this case, however, the resulting steel plate suffers degradation in its cold crack sensitivity and/or toughness. Thus, wear resistant steels with improved low temperature toughness and/or toughness have been developed.
For example, JP3273404B (PTL 1) discloses a thick wear resistant steel with high hardness and high toughness, and a method for manufacturing the same, in which the steel having a composition containing 0.20% to 0.40% of C, Si, Mn, low P, Nb, B, and at least one of Cu, Ni, Cr, Mo, V, Ti, Ca, and REM is subjected to reheating and quenching so that a uniform distribution of high hardness and high toughness can be obtained in the thickness direction of the steel, and a central part in thickness direction of the steel has a martensite dominant microstructure with ASTM austenite grain size number of 6 or more.
JP4238832B (PTL 2) discloses a wear resistant steel plate that has a composition containing 0.15% to 0.30% of C, Si, Mn, low P, low S, and Nb, and satisfying a parametric expression formed by at least one element of Cu, Ni, Cr, Mo, V, Ti, and B, and has a reduced difference in hardness between a surface layer part and an internal part of the steel plate and Charpy absorption energy at −40° C. of 27 J or more, in order to guarantee abrasion resistance and workability in a low-temperature range, and a method for manufacturing the same.
JP4259145B (PTL 3) discloses a wear resistant steel plate with excellent low temperature toughness and a method for manufacturing the same, in which the steel plate having a composition satisfying a parametric expression formed by 0.23% to 0.35% of C, Si, Mn, low P, low S, Nb, Ti, B, and at least one of Cu, Ni, Cr, Mo, and V is subjected to reheating and quenching so as to have a martensite dominant microstructure with a grain size of 15 μm or less, resulting in abrasion resistance and Charpy absorption energy at −20° C. of 27 J or more.
JP4645307B (PTL 4) discloses a wear resistant steel plate with excellent low temperature toughness and a method for manufacturing the same, in which a steel having a composition containing 0.23% to 0.35% of C, Si, Mn, low P, low S, Cr, Mo, Nb, Ti, B, and REM, and satisfying a parametric expression formed by at least one element of Cu, Ni, and V is subjected to hot rolling to obtain a steel plate, which is then subjected to direct quenching so as to have a martensite dominant microstructure with a grain size of 25 μm or less resulting in abrasion resistance and Charpy absorption energy at −20° C. of 27 J or more.